Communication system



. Jan. 13, 1942. Y

c. Bx-:vooR-r 2,270,104

COMMUNICATION SYSTEM Filed July 29, 1939 Patented Jan. 13, 1942 COMMUNICATION SYSTEM Cornelis Bevoort, Amsterdam, Netherlands Application July 29, 1939, Serial No. 287,210 In the Netherlands August I0, 1938 20 Claims.

The present invention relates to communication systems in which voice or other communica-V tion signals are transmitted from two transmitting stations to a receiving station. The system herein disclosed embodies improvements which enable the receiving station to remain in simultaneous communication with both transmitting stations for the reception of signals transmitted either alternatively or simultaneously from the two transmitting stations; also which enable the intensity or volume of the signals from the two transmitting stations to be relatively proportioned at said receiving station so that the signals from both transmitting stations are of approximately the same intensity at the receiving station.

One advantageous embodiment of my invention pertains to the recording or reproducing of telephone conversations transmitted over a two-Way communication system. In the recording of telephone conversations transmitted back and forth between two stations, problems are likely to arise by reason of the wide variations of volume or intensity of signal strength acting on the recording medium, particularly as between the signals from a station which is near at hand and the signals from a station which is a considerable distance away. It is a fact Well known in the recording of sound, particularly on phonograph records, that the intensity or loudness of the signal acting on the recording medium must not be permitted to vary between excessively wide limits. Myimproved system meets this requirement by relatively -proportioning the signal strength reaching the recording medium from each of the two transmitting stations, whereby the signals from both of these stations are of approximately the same intensity at the point where they perform the recording operation. This aspect of the invention is also advantageous in situations where recorded conversations or other recorded material is reproduced by the system, and, likewise, in situations where a two-way communication system employs a radio link. My improved system herein disclosed effects the above-described volume control without causing an objectionable degree of attenuation -in the twowire connection between the two transmitting stations, such as has been an objectionable characteristic of prior devices.

Another advantageous embodiment of the invention is in connection with radio and telephone communication systems on airplanes and the like, wherein radio signals are transmitted over a radio vchannel between a ground station or other transmitting station and the radio operator on the plane, wherein the voice signals resulting from said radio signals are transmitted to the pilot of the plane via the radio operators control, and wherein the voice signals originated by the pilot are also transmitted via the operators control. My improved system enables the radio operator on the plane to maintain simultaneous connection with both channels, and to control the intensity or strength of the signal reaching his receiver from either source.

Other objects, features, and advantages of the invention will appear from the following detail description of one preferred embodiment thereof. In the accompanying diagram which schematically illustrates this embodiment, the two transmitting stations or other signal emanating devices are indicated at Aand B, and the receiving station or like signal responsive device is indicated at C. A network having four pairs of terminals serves to operatively connect these three stations A, B, and, C, and also serves to establish connection with an artificial or balancing line which includes the variable resistance or impedance R, as will be later described. In situations where disproportionate signal strength is likely to be in one direction at one time' and in another direction at another time, I preferably connect the network with the transmitting stations A and B through the instrumentality of the transposing or reversing switch S, which enables the necessary transposition to be made when the greatest or excessive signal strength comes from A instead of B, or from B instead of A. In the illustrated position of the switch S, the greater signal strength is in the direction from B to A. 'I'his transposing switch comprises the four springs or movable switch elements 4, 5, 6, and 1 which are all gang connected for simultaneous movement. Disposed on opposite sides of the respective spring elements are associated contacts la-lb, 5a-5b, etc. Station A is connected with contacts la and 5a. Station B is connected with contacts 6b and 1b. Cross connections are established between contacts la and 6a, between contacts Ib and 6b, between contacts 5a and 1a, and between contacts 5b and 11:. The switch blades 4--5 are connected with the pair of terminals I04-II of the aforementioned network, and the other two switch blades 6--1 are connected with the pair of network terminals designated I2-l3. The receiving unit C is connected with the pair of network terminals H-I, and the articial line I8 is connectedwith the fourth pair of network terminals I6--l1. The artiilcial line I8 includes the adjustable resistance R.

In -the preferred embodiment of the invention, the network comprises a hybrid transformer set T made up of two transformers I2 and 2l. The transformer i9 comprises' two main windings, or two sections of a single main winding. indicated at 2 I-2I which are serially connected with the terminals i2-i3. This transformerA il also comprises two separate coupling windings 22- 23 which are inductively'related to the main winding 2i-2l through the core of this nrst transformer. The other transformer 2l likewise comprises two main windings, or two sections of a single main winding, indicated at 2|- 24, which are serially connected with the terminals il-l5. Similarly, this other transformer 20 also includes two separate coupling windings 2526 which are inductively related to the main winding 24-24' through the core of this second transformer. The first pair of coupling windings 22 and 25 of the two transformers are connected in series relation with each other and with the first pair of network terminals IU-I i. The second pair of coupling windings 2l and 25 of the two transformers are also connected in series through the terminal network Il-I'I which includes line i8 with its resistance R. It will be noted. however, that one of the windings of this second pair is wound or connected reversely with respect to the companion winding of the first pair. This reverse relationship is schematically indicated in the drawing. 'I'he effect thereof is that the two pairs of coupling windings 22, and 23, 26 will act in opposition to each other, the second pair 23, 26 bucking the coupling efl'ect of the first pair 22, 25; This bucking effect of the second pair can be varied as desired by adjusting the resistance R in the artificial line i8.

In situations where the system or apparatus is used for recording telephone conversations, the stations A and B represent any two telephone stations adapted to conduct a two-way communication therebetween over the line a-b. The receiving device C will then include suitable recording apparatus, feitherof the phonographic disk type, photoelectric cell and film type, or any other preferred type. Ampliers or other controllable devices may be included in the unit C, or may be interposed-in the circuit between this unit and the terminals |4-i5. Assuming that the greatest signal strength is from station B,

` the transposing switch S is placed in the position shown, with station B connected to main winding 2i-2I, and with station A connected to the two coupling windings 22, 25. If, on the other hand, the greatest signal strength is from station A, then the transposing switch S is thrown to the other position, which connects station A with main winding 2 I-2i', and which connects station B with the two coupling windings 22, 25. Having placed the transposing switch S in the proper position corresponding to the direction of greatest signal strength, the resistance R in the simulating network i8 is then adjusted so that the signals from both stations A and B are of approximately the same intensity at the point where they perform the recording operation in station C. The transfer of signal from the Amain windings 2i-2l' to the other main windings 24-24' is so controlled by the variable resistance R that the intensities received from the two directions A and B are substantially equal.

The attenuation between the two line pairs of terminals Ill--Ii and i2-i3 is relatively small. m

Practical use of the apparatus has shown that this transfer attenuation introduced between stations A and B is almost negligible. being of the order of approximately 0.4 nepers. The attenuation between the line pair of terminals |2-I3 and the receiver pair of terminals il-IB is made controllable by adjustment of the artificial line il. This artificial line serves to attenuate the signal received from the source of the stronger signal and thereby renders the signal strength from both sources substantially equal.

The use of the apparatus and the mode of operation thereof in situations where recorded conversations or other recorded material is reproduced on the system, will be apparent from the preceding description. Also, as previously remarked, the apparatus can be employed in situations where the receiving unit or station B embodies a radio transmitter for transmitting in a broadcast or otherwise the complete conversation or two-way communication occurring between. the two transmitting stations A and B of the system. In each of the above-described embodiments of the invention, it will be understood that the station or unit C may include a headset, speaker, volume meter, or other suitable instrumentality for indicating the signal strength at this station.

When the invention is included as a part of the radio and telephone communication systems used on airplanes and the like. particularly on planes having a radio operator in addition to the pilot, station A may be considered as the microphone for the pilot, station B may be considered as the radio receiving set for the plane, and station C may be considered as the headset for the radiooperator. It will be seen that such arrangement leaves the radio operators headset C simultaneously connected with both the pilot's microphone A and with the plane's receiving set B for reception of any messages transmitted either alternately or simultaneously from both sources. Should it be desired to reduce or proportion the intensity of the signals from one of these sources, such can be readily effected by appropriate adjustment of the transposing switch S and by appropriate adjustmentof the variable resistance R, substantially as previously described.

In each of the above-described embodiments. the transposing switch S and the variable or adjustable resistance R may be arranged foi separate actuation; or, alternatively, they may be coupled together in such manner that adjusting the resistance R will throw the switch S automatically when a certain point of adjustment is reached. Such a coupling connection is diagrammatically indicated at 28. It is also understood that the movement of the adjustable member of resistance R may be correlated with other parts of the receiving or transmitting apparatus, at the disposal of the operator, to thereby simultaneously adjust the volume of received or transmitted signals.

Instead of having the transposing switch S connected between the line parts a and b, it may be connected between every other pair of the four connected elements, i. e., the line parts a and b, the apparatus C, and the artificial line i8. Furthermore, instead of the hybrid set T, other equivalent multiple pole networks may be used. For example, the hybrid transformer may be replaced by any other eight-pole network. It may also be replaced by a network having a less number of poles. particularly when, within the netformer -set connecting said transmitting deviceswork itself, means are already present which fulfill the function oi the impedance R. 'I'he number of poles required may also be obtained by suitable combination of connecting terminals.

Accordingly, it will be seen that while I have illustrated and described what I regard to be the preferred embodiment of the invention, nevertheless it will be understood that such is merely exemplary and that numerous modifications and rearrangements may be made therein without departing from the essence of the invention.

I claim:

1. A circuit for recording or reproducing speech on a two-wire line which is adapted to establish two-way communication between two stations each having transmitting and receiving equipment, the recording or reproducing apparatus being tapped into said line at a point between said stations, the speech varying in intensity with the direction of transmission, the intensity of the recording or reproducing apparatus having to be as constant as possible, characterized in that at the tapping point the line is cut into a leftand a righthand part, a network having at least three sets of terminals being provided at this point, the attenuation being small between two sets and controllable between one of these sets and the third set, the line parts being connected to the first mentioned sets and the apparatus to the third set, such that the transfer attenuation between the two line parts is small, and is controllable between one of these line parts and said recording or reproducing apparatus.

2. A circuit according to claim 1 characterized in'that the network has a further set of terminals to which a controllable impedance is connected for ontrolilng the impedance between the sets of terminals mentioned in claim 1.

3. A circuit according to claim 1 characterized by a switch so arranged in at least two of the connections between the network and the connected elements that in one position the attenuation between one line part and said apparatus is controllable and-in another position the attenuation between the other line part and said apparatus is controllable.

4. In a communication system of the class described, the combination of a plurality of stations each having transmitting and receiving apparatus therein, a line connecting with said stations for establishing two-way communication therebetween, a; receiving device, and a network connecting `with said line enabling said receiving device to receive signals from said transmitting apparatus of both stations, said network comprising means for relatively proportioning the intensity of the signal strength reaching said receiving device irom each transmitting apparatus.

5. In a communication system of the class described, the combination of a plurality of stations each havingtransmitting and receiving apparatus therein, a line connecting with said stations for establishing two-way communication therebetween,v a receiving device, and a network tapped into-said line enabling said receiving device to receive signals from said transmitting apparatus of both stations, said network comprising an articial line. including a variable impedance for relatively proportioning the intensity of the signal strength reaching said receiving device fromy each transmitting apparatus.

6. In a communication system of the class described, the combination of a plurality of transmitting devices from which signals are transmitted, a signal receiving device, a hybrid transwith said receiving device, and manually actuated means for varying the intensity of the signal strength between said transmitting and receiving devices.

A 7. In a communication system of the class described, the combination of a plurality of transmitting devices from which signals are transmitted, a signal receiving device, a hybrid transformer set connecting said transmitting devices with said receiving device, and manually controllable means cooperating with said hybrid set for relatively proportioning the intensity of the signal strength reaching said receiving device from said transmitting devices.

8. In a communication system of the class described, .the combination of a plurality of stations each having transmitting and receiving apparatus therein, a line connected to establish twoway communication between said stations, a signal receiving device, and a hybrid transformer set connecting said line with said receiving device, said hybrid set comprising a plurality of main windings, and coupling windings for inductively coupling said main windings, one of said main windings and one of said coupling windings being connected with said stations and another of said main windings being connected with said receiving device.

9. In a communication system of the class described, the combination of a plurality of stations each having transmitting and receiving apparatus therein, a line connected to establish twoway communication between said stations, a signal receiving device, and a hybrid transformer set tapped into said line for connecting the transmitting apparatus of both stations with said receiving device, said hybrid set comprising a plurality of main windings, separate coupling windings for inductively coupling said main windings, two of said coupling windings being arranged to oppose each other, and adjustable means for controlling the current ow through one of said coupling means.

10. In a communication system of the class described, the combination of a plurality of transmitting devices from which signals are transmitted, a signal receiving device, a network for connecting said receiving device with one of said transmitting devices in one ratio of transformation, and for connecting said receiving device with another of said transmitting devices in another ratio of transformation, and switch means connected between said transmitting devices and said network for reversing said transmitting devices with respect to said ratios of transformation.

11. In a circuit of the class described, the combination of a network having four pairs of terminals and means for coupling said terminals together inductively, signal transmitters connected with two of said pairs, a signal receiver connected with a third pair of said terminals, and a variable resistance connected with the fourth pair and operative through said inductive coupling means for varying the signal strength received by said signal receiver from one of said transmitters, said network connecting said receiver to one of said transmitters in a relatively high volume relation, and connecting said receiver to another of said transmitters in a relatively low volume relation.

12. In combination, two signal transmitting stations A and B, a signal receiving station C comprising recording apparatus, `and a. hybrid transformer set for connecting said stations, comprising two transformers including two main windings and first and second pairs of coupling windings inductively coupling Vsaid main windings, switch means for alternatively connecting said transmitting stations A and B with one of said main windings and with said yfirst pair of coupling windings, said receiving station C being connected with said other main winding, said second pair of coupling windings being adapted to buck said first pair of coupling windings, and means for adjusting the current fiow through said second pair of coupling windings.

13. In a communication system of the class described, the combination of two main stations A and B each having transmitting and receiving apparatus therein, a two-wire transmission line connecting said stations for establishing twoway communication back and forth therebetween, a receiving station C adapted to receive the twoway communications transmitted back and forth between stations A and B, a network for establishing a tapped connection between said transmission line and receiving station C, the point of tapping of said network with said transmission line dividing said line into left and right hand parts, said network comprising a hybrid transformer set including two transformers having first and second main windings and having first and second pairs of coupling windings which inductively couple said main windings together, the two parts of said transmission line being connected with said rst main winding and with said first pair of coupling windings, said receiving station C being connected with said second main winding. an artificial line connected with said second pair of coupling windings, an adjustable resistance connected in said artificial line for adjusting the current flow through said second pair of coupling windings, said second pair of coupling windings being adapted to buck said first pair of coupling windings, and a reversing switch for reversably connecting the left and right hand parts of said transmission line with said first main winding and with said first pair of coupling windings.

14. In a communication system of the class described, the combination of two main stations A and B each having transmitting and receiving apparatus therein, a two-wire transmission line connecting said stations for establishing twoway communication back and forth therebetween, a receiving station C adapted to receive the twoway communications transmitted back and forth between stations A and B, a network for establishing a tapped connection between said transmission line and receiving station C, the point of tapping of said network with said transmission line dividing said line into left and right hand parts, said network comprising a hybrid transformer set including two transformers having first and second main windings and having first and second pairs of coupling windings which inductively couple said main windings together, the two parts of said transmission line being connected with said first main winding and with said first pair of coupling windingsfsaid receiving station C being connected with said second main winding, an artificial line connected with said second pair of coupling windings, said latter pair of coupling windings being adapted to buck said first pair of coupling windings, and a reversing switch for reversably connecting the left and right hand parts of said transmission line with said nrst main winding and with said first pair of coupling windings.

15. In a communication system of the class described, the combination of two main stations A and B each having transmitting and receiving apparatus therein, a two-wire tion line connecting said stations for establishing two-way communication back and forth therebetween, a receiving station C adapted to receive the two-way communications transmitted back and forth between stations A and B, a network for establishing a tapped connection between said transmission line and receiving station C, the point of tapping of said network with said transmission line dividing said line into left and right hand parts, said network comprising a hybrid transformer set including two transformers having first and second main windings and having first and second pairs of coupling windings which inductively couple said main windings together, the two parts of said transmission line being connected with said first main winding and with said flrst pair of coupling windings, said receiving station C being connected with said second main winding, an artificial line connected with said second pair of coupling windings. and an adjustable resistance connected with said artificial line for adjusting the current ow through said second pair of coupling windings, said second pair of coupling windings being adapted to buck said first pair of coupling windings.

16. In a communication system of the class described, the combination of two main stations A and B each having transmitting and receiving apparatus therein, a two-wire transmission line connecting said stations for establishing twoway communication back and forth therebetween, a receiving station C adapted to receive the two-way communications transmitted back and forth between stations A and B, a network for establishing a tapped connection between said transmission line and receiving station C, the point of tapping of said network with said transmission line dividing said line into left and right hand parts, said network comprising a hybrid transformer set including two transformers having first and second main windings and having first and second pairs of coupling windings which inductively couple said main windings together, the two parts of said transmission line being connected with said first main winding and with said first pair of coupling windings, said receiving station C being connected with said second main winding, and said second pair of coupling windings being connected together in such relation as to buck said rst pair of coupling windings.

17. In a communication system of the class described, the combination of two main stations A and B each having transmitting and receiving apparatus therein, a two-wire transmission line connecting said stations for establishing two-way communication therebetween, a receiving station C adapted to receive the two-way communications transmitted back and forth between stations A and B, and a network for establishing a tapped connection between said transmission line and receiving station C, said network comprising a hybrid transformer set including two transformers having first and second main windings and having first and second pairs of coupling windings which inductively couple said main windings together, said transmission line being connected with said first main winding and with said nrst pair oi coupling windings, said receiving station B being connected with said second main winding, and means cooperating with said second pali: of coupling windings for adjusting the Icoupling effect between said transformers.

18. In a communication system of the class described, the combination i two main stations A and B. a transmission line connected with said stations for establishingtwo-:way communication therebetween, a receiving station C adapted to receive signals transmitted in either direction over said transmissionline between stations A stations, a transmission line connected with said stations for transmitting signals from one of said stations to the other, a receiving station adapted l-to. receive said signals, and a network tapped into said transmission line for establishing a coupled relation between said stations,

said network comprising means for substantially maintaining the eiiectiveness oi said transmissionline to transmit signals between said transmitting stations with relatively small attenuation, and means for controlling the attenuation between one oi the parts of said transmission line and B, and a network taped into said transmission line for establishing a coupled relation between stations A, B, and C, said network comprising means for substantially maintaining the effectiveness of said transmission line to transmit signals between stations A and B with relatively small attenuation while station C is also receiving said signals,l and means i'or varying the transferattenuation betv'leen one oi the parts of said transmission line and said receiving station C.

19. In a communication system oi the class described, the combination of two'transmitting 

